Wastewater treatment systems rely upon a network of underground pipes, e.g. sewer lines, for delivering waste water to the treatment plants, either through gravity flow, or a combination of gravity flow and pumping stations. Typically, such systems consist of main lines running underground, beneath streets, and lateral lines extending from the mains to the buildings being served. Thus, in any given city or suburban location, many miles of sewer lines exist underground as an essential part of the wastewater treatment system. Generally, the mains are maintained by the municipality or private system owner, while the laterals are the responsibility of the property owner.
The pipes used for the various underground lines are typically of several different materials, such as concrete, ductile iron, terra cotta, or other well known and often used materials. The pipes have a number of joints, typically of the bell and spigot type, with packing to ensure the fluid tightness of the joint. Over time, however, the material forming the joints will decay or will become brittle and crack, causing leaking joints. The shifting and settling of the ground around the pipes also is a major cause of damage to the joints, and additionally, in the case of lateral lines, nearby excavations or tree roots commonly cause shifting of the lines, breaking the pipes and/or the joints. Further, tree roots can penetrate the lines, and faulty installation of new lines is also a significant cause of leakage.
Such damage to sewer lines is a serious problem in a great many areas throughout the country, for several reasons. Firstly, the presence of leaks in the sewer lines, while not generally allowing sewage to flow out into the ground, does allow a large quantity of groundwater to enter the lines. In older areas, particularly ones with aging sewer lines, a large volume of water enters the sewage treatment system, and the volume of water treated is increased, thus increasing the overall cost of the treatment plant. This problem is often referred to as "infiltration and inflow" or simply "I & I". In more modern waste treatment systems using secondary and even tertiary treatment systems, considerable cost is incurred in treating groundwater, which otherwise would not need to be treated, particularly by secondary or tertiary methods. The result is ever increasing costs for such treatment.
Secondly, the cost of repairing such lines is itself a sizeable factor in the operating budget for such systems. To repair a sewer line located beneath a street, the precise location of the leak must be determined. Typically, this would require a large excavation, necessitating closing of the street in whole or in part, to simply locate the leak. Then, either a large section of the pipe must be removed and replaced, or perhaps a patch can be applied directly to the leaking area of the pipe. The equipment and labor costs involved in such repair work are quite high, and the disruption of the ordinary use of the street can be a great problem in many cities.
More recently, efforts have been made to locate the leaks in such lines by using a television camera which is mounted on a dolly, to travel through the line and display an image of a leak site to the operator. The operator can then locate more precisely the leak and source of the inflow, and the repair may be done from inside or outside the pipe. However, when the repairs are done on, or from, the inside of the pipe, they are typically less suitable, and the life of the repair is usually shorter, since the water is tending to flow inwardly, rather that outwardly, and the hydrostatic pressure can become great, disrupting or dislodging an internal patch. While the cost of repairs to a line from the inside is generally lower than the cost of excavating the pipeline, in many cases internal repair is not suitable, such as in the case of very large quantities of inflowing water, i.e. when the line is adjacent to flowing groundwater, which can wash out a repairing compound before it has the time to set or cure.
Other efforts are made to seal the leaks on the outside of the pipe, by applying various sealants or patching materials/products to the pipe joint, or to the area of the pipe surrounding the leak. However, in such operations, care must be taken to avoid the use of materials which would contaminate soil and groundwater, causing still further problems. In the past, quite often bituminous products have been applied to the outside of the pipe to seal leaks. Such products, however, usually will introduce groundwater contaminants into subterranean strata, and such contaminants can travel great distances in the aquifers. The deleterious effects of the use of such materials may not be felt for some years later.
Further, any external technique which requires a large excavation will of necessity cause a disruption in ordinary surface activity, and if the pipe is beneath a main roadway, such disruptions can be a major problem. Also, the existence of other utility lines, such as electric or water lines proximate the sewer lines, can cause further problems with excavation techniques using conventional excavation equipment. Thus, caution must be exercised when doing excavation work, so that the operator does not damage other lines while trying to dig to the sewer line.
Additionally, since sewer lines are often quite deep, requiring a deep excavation, considerable shoring is needed to prevent collapse of the excavation. Thus, the excavation size is generally considerably greater in width than the sewer line, often 10 feet or more in width.
Another problem with prior repair techniques is associated with the fact that it is difficult to determine whether the leak has been sealed before the excavation is backfilled and restored to normal condition. The hydrostatic pressure will not again be exerted on the pipe until after the backfilling has been completed. Thus, if the leak is not properly sealed, it will be necessary to redo the work. Also redoing the work will require removal of the materials previously used. If concrete or other hardenable material was used as the sealant, or if patches with clamps were used, the job is made even more difficult.
Similarly, no suitable technique has heretofore been developed in which only a small excavation is needed, and by which a leak may be properly and suitably repaired.
Prior art techniques have been proposed for overcoming some of the many problems pointed out above, but such techniques have met with only limited success. Thus, U.S. Pat. No. 3,084,719 to Wallace et al discloses a technique which utilizes a plurality of holes drilled into the earth along a sewer line. The technique does not locate the leak precisely but instead drills a number of holes along the line to in effect seal the entire line, leak and all. Next, the patentee injects a quantity of a low viscosity road oil into the holes, and applies a pressure to this oil to "crack" or "break" the soil between adjacent holes. Then, a quantity of a second sealant, an asphaltic emulsion, is forced into the holes so as to travel between adjacent holes and through the fractured formation. The emulsion then sets, hopefully sealing the leaks in the pipe.
One of the major drawbacks of this technique relate to the introduction of large quantities of petroleum based products into the soil, the groundwater and the sewage in the lines. Another drawback is the fact that the sealing is less than certain. If the leak is not sealed the hardened asphalt emulsion around the pipe will make further repairs even more difficult. Further, if any of the sealant enters the sewer line, it is quite possible that the sealant will harden in the sewer line, causing blockage therein. Another drawback is the drilling of multiple holes which can be just as disruptive as one large excavation, damages the roadway in several places and increases the possibility of damaging another utility line.
Another solution was proposed in U.S. Pat. No. 2,917,085 to Douse. Here, the patentee also formed a number of small holes through the ground to the vicinity of the leak, and then injected a quantity of cement into the hole. When the cement was hardened, the leak would be stopped. Once again, however, it is difficult to determine whether the leak has stopped. If not, re-excavation would be considerably more difficult because of the hardened cement in the vicinity of the leak.
Still a different technique is disclosed in U. S. Pat. No. 4,094,150 to Clarke, which uses a gel-forming composition in the earthen formations around sewer pipe joints to prevent groundwater infiltration. The composition is a mixture of a monomeric acrylamide, N,N'methylenebisacrylamide, a diatomaceous earth, a water soluble metal salt and a catalyst such as mixture of ammonium persulphate and sodium thiosulfate in aqueous solution. The water, diatomaceous earth and catalyst are mixed separately from the resins, and once mixed, the composition is said to gel in about 20-30 seconds. The composition is used as a grout around bell and spigot joints or other joints. Because of the short time available after mixing, the material must be placed very quickly around the joint. For this reason, its is likely that this composition could only be applied around a fully uncovered pipe, with a worker down in the excavation. Further, the short time after mixing can lead to a variety of handling equipment problems.
Accordingly, a primary object of the present invention is to provide an improved, simplified method for the sealing of leaks and prevention of infiltration into underground utility lines.
Another object of this invention is to provide a method for preventing infiltration which does not require a large excavation.
A further object of the invention is to provide a method for preventing infiltration into sewer pipes which will not cause groundwater and/or soil contamination.
Yet another object of the invention is to provide a method for preventing infiltration of groundwater into sewer pipes which can be quickly and easily verified.
Still another object of this invention is to provide a method for sealing leaks into sewer lines which can be easily repeated in the event that a leak is not completely stopped.
Yet a further object of the invention is to provide a low cost technique for stopping inflow and infiltration into sewer pipes.
A still further object of the invention is to provide a method for preventing infiltration into sewer pipes which uses readily available, low cost materials.
Another object of the invention is to provide a very effective method for preventing infiltration into sewer pipes which uses relatively unskilled labor, in combination with low equipment costs and low material costs.
Still another object of the invention is to provide an improved method for preventing leaks into sewer lines which can tolerate some settling and shifting without damaging the repaired area.
Still a further object of the invention is to provide a method for preventing leaking into sewer pipes with but small and minor disruption to the surface, thereby reducing long term road maintenance costs.
These and other objects and advantages of the present invention will become apparent from the further description of the invention which follows.